Back in the late 1980s some manufacturers like Araya and Wolber added numbers to some high performance clincher rims to denote the "naked" rim weight. For example, the Araya CTL-370 rim weighed 370 grams, nekkid, one of the lightest aluminum clincher rims made. Other Araya and Wolber clincher rims had 4xx (numbers in the four-hundreds) to denote bare rim weight. The data for those rims -- PDFs and photocopies of old catalogs -- may be found in the archives of those websites, although the Araya data is buried in the Araya Japan site and not easy to find.
Keep in mind these rims were somewhat fragile at the time and may have lots of miles and years on them now. They were usually gray hard anodized aluminum, low profile. They could be finicky and needed tweaking once a week or so to true the wheels (depending on mileage, terrain, rider weight, etc).
I liked those Araya CTL-370 and Wolber Alpine Super Champion rims, which were standard on 1980s Centurion Ironman bikes, but both rear rims cracked at the spokes a couple of summers ago. The front wheels are still fine. Eventually I'll replace the rear wheels with comparable lightweight low profile rims, but I'll be more diligent about maintenance. Some folks recommend stripping the wheels of the tires, tubes and rim strips, de-tensioning the rims, then re-tensioning and tuning them only on a wheel truing stand, using a spoke tension gauge. I didn't do that and probably contributed to the rim failures. Or maybe they would have failed anyway after 30+ years.
For carbon fiber rims I just visit the manufacturers' websites.